App.net, the ad-free social network founded by Dalton Caldwell, introduced private messages for its users last month, and now Felix has become the first mobile app to take advantage and ship with the feature.

At $4.99 Felix isn’t the kind of download that you’ll grab on a whim but the latest version of the iOS app does a lot more than just allow Twitter-style Direct Messaging. Felix 1.3 has a very nifty full-screen mode — activated by pinching in on the screen, deactivated by pinching out — and it also features a bunch of new swipe gestures which (after taking a little time to master) make navigating the app a real joy.

Direct messages through Felix is easily done. Just visit a user profile, select the messages icon, then choose to send a private message.

Unlike Twitter, App.net users can message anybody on the service — Felix creator Bill Kunz, for example, doesn’t follow me but I am able to reach his inbox. That system works fine among App.net’s comparatively small userbase — since users must pay to join and that’s created a level of shared trust — but would bring obvious issues to free services like Twitter.

Felix’s new full-screen mode is great for mobile devices. These screengrabs are from an iPhone 4 but the iPhone 5’s larger screen would make greater use of this extra space. Interestingly, Kunz says that future updates will remove the navigation bars altogether, and more gestures will be forthcoming — you can read more on his plans below.

Explanations for the two finger gestures load on arrival and can be summoned at any time by simply shaking your device while it is in full-screen mode.

Not only is it slick to use and beautifully designed, but the app comes with a range of built-in support for media and read-later services. While I’m not as active on App.net as I am on Twitter, I’ve been keeping tabs on its progress. I began using Appapp and the basic Web app client but have most recently used a combination of Rivr (review), Felix, and Adian. There are a tonne of other apps out there, but I’m certainly impressed enough with Felix that I won’t be moving elsewhere for the foreseeable future.

Full private messaging support. Enjoy first-class private messages with your friends! (And yep, amigos, you can attach images and use custom links in private messages, just like in regular posts.)

Protip: The post button moved to the top right of most screens. For now …

A brand new way to play – full-screen mode is here, with plenty of gestures to make it even more fun. Activate full-screen mode by “pinching out” with two fingers, or turn it off by pinching in. Need a reminder of what gestures do what? Shake your iPhone or iPod when in full-screen mode for tips.

Full-screen mode is just getting started – I want to learn from how you use it. So give it a try and let me know! The best way is through email – go to the Dashboard tab, “Settings and Information”, then “Felix Support”.

A bunch of little bits of polish and tweaks here and there.

I shot an email to Kunz, the one man operation behind Felix, who explained his thinking behind the app. Kunz says he is building a service that is focused on discovery, enabling users find content that they wouldn’t ordinarily come across via those users they follow and the interactions they have:

From the beginning, I’ve wanted to break out of the Twitter-like mold of “here are your followers, mentions, and everything else.” If we think of posts as water: the global “universe” of posts would be like the ocean. Posts from you who follow would be a massive river, your mentions a smaller one, and your private messages an even smaller one. Most Twitter (and App.net) clients are based on these basic sources of content.

I think there’s another step that can be taken, and the tools to do so are coming out now. There are currents in the ocean that one might find interesting. Sometimes one may only want to focus on part of that big “who I’m following” river. Maybe there are other rivers entirely you want to check out. I’d like to shake up what people are reading, while at the same time embracing the connection- and conversation-oriented culture that’s thriving at ADN.

You can see some of that shift in the current UI for Felix. Shedding the scaffolding of old conventions to create some new metaphors. The new full-screen mode is just a first step, and certainly isn’t “done.” Over the next few releases, the bottom tabs and top navigation will disappear entirely, and the current gestures for navigation will expand and be enhanced by some upcoming controls. (The current gestures are largely placeholders.)

Kunz explains that, as the single person behind the product, he is constantly updating the app and making changes, rather than “hunkering down for a couple months, radio silent, to make a big splash”. For that reason the app has a new UI that wasn’t present when it was first released in August, and users can expect more changes to come soon.

Kunz is particularly excited by the potential of public channels, which are currently being tested via Patter. He says he is working to integrate the channels — which allow chat room-like messaging for groups — into Felix, so we can expect that soon too.

I believe that these channels will become an important part of the ADN ecosystem shortly and intend to take full advantage of them over time. Entire communities can now create homes for themselves; in time, they could be at least as important as who one “follows.”

As well as being multifunctional and well designed, Felix is an app that is continually pushing the barriers and exploring new avenues where the App.net service can develop. For that reason alone, it is a service that App.net regulars should strongly considering getting their hands on, assuming that they haven’t already.

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